The valve lifter with a variable lift mechanism having the above configuration has to be deployed at a predetermined angle with respect to the cam unit.
One reason is to prevent the cam and the valve lifter from colliding with each other. If the valve lifter rotates around the reciprocating axis and changes the direction thereof, the high lifter deviates from its fixed position and in the case where the internal combustion engine is driven using the low lift cam, the high lift cam comes off the high lifter and crashes into the low lifter to be destroyed.
A second reason is to prevent an oil feeding passage from deviating in position. In the valve lifter with a variable lift mechanism having the above configuration, a cam switching mechanism of the valve lifter is operated by feeding hydraulic pressure from the side of the engine and if the valve lifter rotates and the direction thereof changes, the position of the oil feeding opening on the engine side and that of the oil receiving port on the valve lifter side deviate from each other, whereby the feeding of oil is hindered and the cam switching mechanism acts up.
For these reasons, the valve lifter needs to be deployed at a predetermined angle with respect to the cam unit, in other words, the valve lifter is required to have directionality relative to the cam unit. Conventionally, these needs are satisfied by providing a detent means in the valve lifter.
For example, in FIG. 14 (FIG. 1 of the patent document identified later), a pin 102 is projected from the side surface of the valve lifter 101 so as to engage with a longitudinal groove 104 formed on the inner surface of a cylinder bore 103. The pin 102 and the longitudinal groove 104 constitute a detent means of the valve lifter 101.
The reference numeral 105 in FIG. 14 designates a center lifter which advances and retracts with hydraulic pressure of an oil passage 106 and when the center lifter is located in a retracted position as shown in FIG. 14, a high lift center cam 108 passes through a slit 107 and a low lift cam 109 comes into slidable contact with a low lifter 110. As a result, a valve 111 is opened and closed with low lift. On the other hand, when the center lifter 105 advances into the slit 107 and locates at an advanced position thereof, the high lift center cam 108 comes into slidable contact with the outer surface of the center lifter and the valve 110 is opened and closed with high lift.
In the thus constituted valve lifter with a variable lift mechanism, the same technical advantages can be obtained as those in FIG. 11 by, contrary to the lifter shown in FIG. 14, providing the pin 102 on the side of a bore and providing the longitudinal groove 104 on the side of the valve lifter. In either case, the detent of the valve lifter can be accomplished by engaging the pin with the longitudinal groove.